1. Field of the Invention
The present invention relates to a composition for forming a silicon-containing resist under layer film used in a multilayer resist method used for fine processing in a step for producing a semiconductor device, and a patterning process using the same.
2. Description of the Related Art
In the 1980s, exposure light whose source is g-beam (436 nm) or i-beam (365 nm) of a mercury lamp was commonly used for resist patterning. To achieve a further micro resist pattern, a method for making exposure wavelength shorter has been regarded as more effective means. In the 1990s, 64 MB (work size: 0.25 μm or less) dynamic random access memory (DRAM) were mass produced, in which short-wavelength KrF excimer laser (248 nm) were employed as an exposure source instead of the i-beam (365 nm). However, the production of DRAMs with an integration degree of 256 MB and 1 GB or more requires finer processing technology (work size: 0.2 μm or less), and needs a light source of shorter wavelength. Amid this technological need, the introduction of photolithography using ArF excimer laser (193 nm) has been seriously studied since about a decade ago. According to initial strategy, ArF lithography was going to be introduced in conjunction with the production of 180 nm-node devices, but a conventional KrF excimer lithography was continuously used until 130 nm-node device mass production. Therefore, official introduction of ArF lithography started with 90 nm-node device production. Meanwhile, mass production of 65 nm-node devices are being promoted by combining with lenses whose numerical aperture (NA) was raised to 0.9. Because of advantageous shorter exposure wavelength, F2 lithography with wavelength of 157 nm was regarded as a next promising production technology for subsequent 45 nm-node devices. However, development of F2 lithography was canceled due to several problems such as higher scanner costs from expensive CaF2 single crystals into projection lenses in large volumes, change in the optical system in accordance with introduction of hard pellicles instead of conventional extremely low durable soft pellicles, and reduced etch resistance of a resist film, thereby introducing ArF-immersion lithography. In the ArF-immersion lithography, water with a refractive index of 1.44 is inserted between a projection lens and a wafer by partial fill method, enabling high-speed scanning. Accordingly, 45 nm-node devices are mass produced by using lenses with an NA of 1.3.
Extreme-ultraviolet (EUV) lithography with wavelength of 13.5 nm is regarded as a next promising fine processing technology by using 32 nm-node lithography. Unfortunately, the EUV lithography is prone to numerous technical problems such as needs for higher laser output, higher sensitivity of a resist film, higher resolution, lower line edge roughness (LER), use of defect-free MoSi laminated mask, and lower aberration of a reflective mirror. Development of another promising 32 nm-node device production technology, high-refractive index immersion lithography, was canceled due to low transmission factor of another promising high-refractive index lens (LUAG) and an inability to obtain a target value of a liquid's refractive index at 1.8. Under the circumstances, general-purpose light exposure technology seems to fail to significantly improve the resolution unless a light source wavelength is changed.
Accordingly, development of a fine processing technology for obtaining a work size exceeding a limiting resolution of an existing ArF-immersion exposure technology has been promoted. As a technology thereof, double patterning technology is being proposed. Specifically, the double patterning technology is a method (method (1)) for forming a first photoresist pattern with an interval rate of a line to a space of 1:3 by using first exposure and development, processing an under layer hard mask by dry etching, laying another hard mask thereon, forming a second line pattern at a space portion obtained by the first exposure by using second exposure and development of a photoresist film, processing the hard mask by dry etching, to form the first pattern and the second pattern alternately. By this method, it is possible that forming a line and space pattern whose pitch is half that of an exposure pattern. Also, there is another method (method (2)) for forming a first photoresist pattern with an interval rate of a line to a space of 3:1 by using first exposure and development, processing an under layer hard mask by dry etching, forming a pattern on a remaining portion of the hard mask by using second exposure by applying a photoresist film on the under layer hard mask, and processing the hard mask by dry etching with the pattern as a mask. In both methods, by processing a hard mask by two dry etching, a pattern whose pitch is half that of an exposure pattern can be formed. Nevertheless, while the method (1) requires formation of a hard mask twice, the method (2) needs one-time hard mask formation, but formation of a trench pattern which is more difficult to resolve than a line pattern.
Another method (method (3)) proposed is to form a line pattern on a positive resist film in X direction by using a dipole light, cure a resist pattern, apply a resist composition thereon again, expose a line pattern in Y direction by using a dipole light, and form a hole pattern from a gap of a grid-like line pattern (Non-Patent Document 1). Moreover, a method for halving a pitch by one-time pattern exposure by using spacer technology in which a resist pattern, an organic hard mask or a polysilicon film whose pattern is transferred and is regarded as a core pattern, and the core pattern is removed by using dry etching, after forming a silicon oxide film around the core pattern at a low temperature, is being proposed.
As mentioned above, finer patterning is difficult only by the upper layer resist, and finer patterning process cannot be established unless a hard mask formed under the upper layer resist is utilized. Under such a circumstance, there is a multilayer resist method as one of the methods to utilize the hard mask as a resist under layer film. In this method, an intermediate film having etching selectivity different from that of a photoresist film, i.e. a resist upper layer film, for example, a silicon-containing resist under layer film is interposed between the resist upper layer film and a substrate to be processed, a pattern is formed to the resist upper layer film, and then, using the upper layer resist pattern as a dry etching mask, the pattern is transferred to the resist under layer film by dry etching, and further using the resist under layer film as a dry etching mask, the pattern is transferred to a substrate to be processed or a film which becomes a core for a spacer process by dry etching.
As a material to be used for such a multilayer resist method, a composition for forming a silicon-containing film has been well known. There are, for example, a silicon-containing inorganic film formed by a CVD method such as a SiO2 film (for example, Patent Document 1, etc.) and a SiON film (for example, Patent Document 2, etc.), and as a material which can be obtained by spin-coating, there are a SOG (spin-on-glass) film (for example, Patent Document 3, etc.) and a cross-linkable silsesquioxane film (for example, Patent Document 4, etc.), etc.
Until now, a resist under layer film which can be used for the multilayer resist method has been investigated, and a composition for forming a silicon-containing resist under layer film as shown in Patent Document 5 or Patent Document 6, etc., has been disclosed. However, in the semiconductor apparatus manufacturing process which exceeds the limit of resolution of the ArF liquid immersion lithography in recent years, a complicated process such as the above-mentioned double patterning, etc., has been proposed. In such a process, a number of lithography processes or a number of processing steps by dry etching is acceleratingly increased; thereby improvement in precision of pattern transferring in the respective coating films has been required. Under such a circumstance, generation of defects in pattern transferring due to the presence of defects in the coated film (coating defects), and lowering in yield thereby becomes a problem. Accordingly, for constructing more rational manufacturing process of a semiconductor apparatus, a composition capable of forming a coating film having less number of defects to the limit for the organic film or the silicon-containing film which is at present practically used has been required.